The device of the present invention generally relates to a new and improved fixture for testing soft packages for leak integrity, and to a new and improved method for testing soft packages for leak integrity.
B. Description of the Prior Art
Since some packaged products can be damaged or destroyed by air or moisture, it is important to ensure that the packages enclosing these products have no leaks. An example of a package preferrably tested for leak integrity is a foil wrapped package. Efforts have been made to provide a nondestructive methodology for evaluation of packaged products of this type to determine if leaks exist.
One of the early standard procedures for detecting leaks in soft packages is an air leak or a bubble detection procedure conducted under water. This test is a destructive test in that the package is pressurized by a hypodermic needle or similar device inserted into the package, and the package is submerged in water at a known pressure. Bubbles from leaks in the package are counted or captured in a graduated container providing an air/time leak rate. This test is often difficult to conduct since very small holes produce bubbles at a very slow rate, thus increasing the opportunity for error.
Another procedure for determining whether there are leaks in soft packages is trace gas detection using positive pressure. A procedure of this type is provided by Inficon Leybold-Heraues. This procedure involves the introduction under pressure of trace gases into a package to be tested. Leakage of the trace gases is then detected. Such a procedure can result in environmental pollution of the test area, and can lead to frequent incorrect positive test results.
Another trace gas test provides detection in a partial vacuum. In this testing procedure, packages are sealed in a trace gas environment and placed in a partial vacuum. The amount of gas released is monitored to determine whether a leak exists. This test is destructive when the package contents are degraded by the gas and requires sensitive and expensive equipment. Environmental pollution of the test area and the item in the package can also occur possibly resulting in false test responses.
Another known procedure for determining leaks, is a vacuum decay test. In this test, a sample is placed in a first chamber of known volume. Pressure is drawn from the first chamber to a second chamber of known volume. As this is being done, the second chamber is measured for decay in vaccum that would be caused by a leak in the package. Although this procedure is very sensitive, it is difficult to use and can be expensive.
Another destructive test is a test sold by T.M. Electronics, Inc. and Skye Equipment Company, Ltd. These tests involve the insertion of a needle or other device into the soft package, air in the package is then withdrawn and the package is measured for air flow into the package. This destructive test is difficult to use, and the equipment associated with the testing is expensive.
Electronic switches are used in another testing apparatus manufactured by Wilco Precision Testers. In this procedure, packages are placed in a vacuum chamber adjacent a plate with an electric switch or proximity sensor adjacent to each package. Pressure in the vacuum chamber is then decreased creating a vacuum and causing packages without a leak or a slow leak to expand. Once the packages expand a predetermined amount, each of the packages engage a switch or proximity sensor. The engaged sensor provides a signal indicating the package has satisfied the test. This testing equipment will not indicate small or marginal leaks in foil packages, since once a foil package expands, the memory of the package material maintains the package in its expanded configuration despite leakage of air from the package. In this situation, the proximity sensors will signal that no leak exists even though there is a leak in the sample package.
Another testing procedure that uses a vacuum to test for package leaks is a Test-A-Pack system manufactured by the Aro Corporation. This system is intended for larger packages and functions properly only when gross dimensional changes of the packages are to be measured. The system is not adaptable for small packages. The Aro system includes no procedure for detecting small leaks, and like the Wilco system, is not sensitive to a small leak.